1. Field of the Invention
The invention relates to an apparatus for bending and tempering glass plates, with a horizontal roller furnace for heating glass plates to the bending temperature, a press bending station following the roller furnace and a cooling station following the press bending station, a flexible conveyor belt being provided between the roller furnace and the cooling station which takes over the glass plate from the furnace roller bed and conveys it into the bending station, in which the glass plate is bent together with the conveyor belt and the bent glass plate is subsequently conveyed into the cooling station.
2. Background of the Related Art
An apparatus of this type is described in DE-AS 14 71 872. The bending press there comprises a convex, upper bending mold and a concave, lower bending mold of conventional construction. Following the bending process, cooling air is supplied to both surfaces of the glass plate in the bending station in order to give it the necessary dimensional stability. This cooling is followed by the actual tempering process in a following cooling station constructed as a tempering station.
This known apparatus only makes it possible to temper glass plates having a thickness of at least 5 mm. If the glass plates are thinner than 5 mm, after cooling for dimensional stability purposes, their interior has already been cooled to such an extent that their temperature is no longer adequate for obtaining the necessary tempering.
DE-AS 12 92 806 discloses a process for bending and tempering glass plates, in which the glass plate in the horizontal position is placed on a soft, resilient mat of nonflammable fabric fixed to the molds of a bending press and during press bending is kept supported on the mat. For the purpose of the subsequent tempering, the molds can be cooled by a fluid medium flowing through them. The mat fixed between the molds can be made from a glass fiber fabric reinforced with metal threads.
In this known process additional means are required in order to transfer the glass plates heated to the bending temperature from the furnace conveying rolls onto the fixed mat. These additional means must be removed from the bending press area following the positioning of the glass plates on the mat. Such a process requires a certain additional time, which leads to a glass plate temperature loss. However, as the glass plate must have a certain minimum temperature for tempering purposes, the plate must be heated to a correspondingly higher temperature in order to compensate for this temperature loss. However, in the case of glass plates thinner than 5 mm, such a more pronounced heating in the preceding roller furnace necessarily leads to problems in connection with the optical properties of the glass plates, due to the increased deformation risk of thin glass plates. In addition, even if a glass fiber fabric is reinforced with metal threads, it has a relatively high heat resistivity, which is prejudicial to a rapid cooling of the lower glass plate surface. Thus, this process is once again only suitable for bending and tempering glass plates with a thickness greater than about 5 mm.